topic Re: more Physical I/Os than Logical I/Os in Operating System - HP-UX

more Physical I/Os than Logical I/Os

Kandaswamy Natarajan — Tue, 05 Jun 2001 18:37:29 GMT

Hi,
I notice on my systems I have more physical I/Os than logical I/Os and the system is running slow.

V2250, 16 GB ram and vxfs filesystems with ORacle database.

Any thoughts Why???

Re: more Physical I/Os than Logical I/Os

A. Clay Stephenson — Tue, 05 Jun 2001 18:50:02 GMT

Sure, I suspect your ORACLE is doing raw I/O
and thus logical i/o's can be less than physical i/o's.

I suspect that you also need to reduce max_dbc_pct as well or set bufpages to about 300-400 MB and thus override dynamic buffer cache. You could then probably increase your ORACLE buffers.

Re: more Physical I/Os than Logical I/Os

MANOJ SRIVASTAVA — Tue, 05 Jun 2001 19:03:19 GMT

Hi Kandaswamy

Oracle needs to be tuned , to reduce the physical reads and ther should be more logical reads.

1.dbc_max to dbc_min difference should be arounf 800mb to 1 gb.
2.Do a sarcheck , go to www.sarcheck.com and downlaod ttheir utility , it take 5 mts to set it up and it give really wonderful results
3. Also I think your real problem is the differnce between what block size oracle is set to and what size your filesystem is set to , incase it is like 16K for oracle and 4 K for Unix then ofcourse you have a problem because for the maintenace oracle works on the block level .

Manoj Srivastava

Re: more Physical I/Os than Logical I/Os

Kandaswamy Natarajan — Thu, 07 Jun 2001 18:49:06 GMT

I have 8 Kb block size set at the filesystem level and 16KB as Oracle db Block size , now do I need to change this values???

Kanda

Re: more Physical I/Os than Logical I/Os

MANOJ SRIVASTAVA — Thu, 07 Jun 2001 18:52:26 GMT

Hi Kanda

Yes Sir , it would involve to recreate the filesystems which is a big pain , unless you are not into production.

Manoj Srivastava

Re: more Physical I/Os than Logical I/Os

Kandaswamy Natarajan — Thu, 07 Jun 2001 19:16:44 GMT

One more concern, I have my Logical volumes stripeed with 64KB stripe size , Will changing these to match with DB block size and filesystem block size help improve the peroformance

Re: more Physical I/Os than Logical I/Os

MANOJ SRIVASTAVA — Thu, 07 Jun 2001 19:41:04 GMT

Hi Kanda

No the 64KB stripe for your logical volumes will not effect the physical read to logical read ration since that goes across a bigger picture , physical disks , contorllers etc .

Manoj Srivastava